My non-scientific, unbacked by anything but my opinion, rectally-derived theory is that the transition from, verb-pronoun / said he, to, pronoun-verb / he said, is tied to:
a) the transition from storytelling being primarily aural (i.e. listening) to primarily visual (i.e. reading). The construction just has a cadence that lends itself to someone speaking and verb-pronoun "feels" like someone telling me a story or performing a story in a pub. "Now, old Johnny McGory wandered down the lane and came across a cow grazing by his gate. That's not my cow, said he and continued on his way, etc..
b) Pronoun-verb is less dialectic and allows for more universal construction of a grammatically correct sentence. As educational standards spread across nations, dialectic construction declined.
I said, you said, he/she/they said -- all grammatically correct.
Said I? Only grammatically correct if you're over the age of 75, with a a pint in one hand. I don't make the rules...
Said you? Them's fightin' words!
Said he/she? All good.
Said they? Feels wrong?
c) the primary aural storytellers of the last 5 decades being stand up comedians where they want to emphasize and/or control cadence, inflection and speed. Verb-pronoun feels constrained while pronoun-verb seems to have more viable inflection options and can be spoken faster or slower with greater control--
he said, HE said, heeeee saaaaaid, he SAID, vs, said he, said HE, saaaaaaid heeeeee, SAID he.